Benzoic acid esters of monohydroalkylcarboranes

ABSTRACT

BENZOIC ACID ESTERS OF MONOHYDROXY-ALKYLCARBORONES IN WHICH THE ALKYL GROUP HAS FROM 1 TO 8 CARBON ATOMS. THE ESTERS HAVE UTILITY AS ULTRAVIOLET LIGHT ABSORBANTS.

United States Patent U.S. Cl. 260476 2 Claims ABSTRACT OF THE DISCLOSUREBenzoic acid esters of monohydroxy-alkylcarboranes in which the alkylgroup has from 1 to 8 carbon atoms. The esters have utility asultraviolet light absorbants.

This is a division of application Ser. No. 397,292, filed Sept. 17,1964, now Pat No. 3,409,663.

This invention concerns certain boron containing esters of aromaticacids, their preparation and their applications.

More particularly this invention relates to esters prepared by thereaction of carborane alcohols and carborane diols with aromatic acids.These esters are generally valuable as intermediates for preparingcarborane derivatives and carborane polymers and in some instances arevaluable as ultraviolet absorbers and protectants.

The term carborane alcohols as used throughout this application is usedto describe compounds containing at least one carborane group as well asone or two reactive hydroxy groups whereas the term carborane diols asused herein describes compounds containing at least one carborane groupas well as two reactive hydroxy groups.

Carborane is the generic term used to describe all the isomers of thedicarbacyclododecarborane of the empirical formula: B H H The termcarboranyl is the name given to the radical of the ortho carboraneisomer shown below:

The ortho isomer is also referred to by the Greek letter theta,abbreviated as 0.

The radical of the para-isomer of carborane is referred to herein asparacarboranyl.

The radical of the meta isomer of carborane is referred to asneocarboranyl, abbreviated as 0.

The term aromatic acid(s) as used throughout this application refers toaromatic acid type reactants having an aromatic nucleus and at least onefree carboxylic acid, acid anhydride, ester or acid chloride groupsattached thereto. In addition to its carboXylic acid or acid chloridesubstituents, the aromatic nucleus can have other substituents, such ashalogen, hydroxy, alkoxy and the like.

It is an object of this invention to prepare novel carborane esters.

It is an additional object of this invention to prepare compositionsuseful as ultraviolet absorbers and protectants.

A further object of this invention is to prepare polymer intermediatesand additives.

The other objects of this invention will become apparent after a furtherperusal of this application.

The above objects among others are achieved through the preparation ofthe esters of this invention.

In practice, a carborane reactant selected from the group of carboranealcohols or carborane diols is contacted with an aromatic acid typereactant as previously described, under the usual conditions ofesterification,

3,574,707 Patented Apr. 13, 1971 namely elevated temperatures anddehydration catalysts.

As the preceding description indicates, considerable variation ispossible insofar as the choice of carborane reactant and aromatic acidtype reactant is concerned.

For example, any of the following illustrative carborane alcohols orcarborane diols can be used as sources of the hydroxyl group; thel-hydroxyalkylcarboranes such as 1-hydroxymethylcarborane,l-hydroxyethylcarborane, the l-hydroxypropylcarboranes, thel-hydroxybutylcarboranes and the like, the 1-hydroxyalkylneocarboranessuch as 1-hydroxybutylneocarboranes, the l-hydroxypentylneocarboranes,etc., the 1,2-bis-(1-hydroxyalkyl)carboranes such as 1,2 bishydroxymethylcarborane, 1,2 bis (hydroxyethyl)carborane, the1,2-bis-(l-hydroxypropyDcarboranes, the1,2-bis-(l-hydroxybutyl)carboranes, etc., as well as thebis-(hydroxyalkyl)neocarboranes. These include bis(hydroxymethyl)neocarborane, bis (hydroxyethy1)neocarborane, the bis-(hydroxypropyl)neocarboranes, the bis-(hydroxybutyl)neocarboranes amongothers. Also included within the scope of carborane alcohols andcarborane diols are those carboranes having a free hydroxy function aswell as other inert functions. For example, carboranes having an etherfunction as well as an alcohol or diol function can be used as thecarborane reactant, illustrative compounds of this type are: bis-(2- Bhydroxyethyl 1 carboranylmethyl) ether, bis-(Z-hydroxymethyl 1carboranylmethyl) ether and the corresponding neocarboranyl ethers. Thefavored carborane reactants are the monoand bis(hydroxyalkyl) carboranesand bis(hydroxyalkyl) neocarboranes wherein the alkyl groups have 1-8carbon atoms. Within this favored group the preferred reactants of thisinvention are the monoand bis(hydroxyalkyl) carboranes wherein the alkylgroup has from 18 carbon atoms. These reactants are preferred becausethe resultant esters are good ultraviolet absorbers and the reactantsare more readily available.

Among the many aromatic carboxylic acid type reactants which can be usedare the following: aromatic monocarboxylic acids including benzoic acid,the toluic acids, the phenylalkylacetic acids such as phenylacetic acidand ,B-phenylpropionic acid, unsaturated aromatic carboxylic acids suchas cinnamic acid, polybasic aromatic carboxylic acids such as phthalicacid and its isomers and the like. Typical aromatic acid halides includethe following: benzoyl chloride, toluyl chloride, phthalyl chloride andthe like. The favored aromatic acid type reactants are the benzoic acidsand the toluic acids, the terephthalic, isophthalic acids, phthalicanhydride and the corresponding acid chlorides.

Further latitude exists in the solvents choice of reaction conditionssuch as the use of temperature, pressure and time used to prepare thenovel compounds of this invention. For example, the esterificationordinarily takes place in the presence of an inert solvent such as thearomatics. When such a solvent is used, i.e. benzene, the water formedduring esterification is taken oif asthe waterbenzene azeotrope using anappropriate apparatus such as a Dean-Stark condenser. When the aromaticcarboxylic acids are used as reactants an esterification catalyst suchas p-toluenesulfonic acid is used as catalyst. Other catalysts includeconcentrated sulfuric acid, anhydrous HCl, HF and the like. When thesesame carboxylic acids are used as reactants, the reactions arepreferably run at the reflux temperature of the inert solvent. However,lower temperatures can be used but the reaction time is substantiallylengthened. Under these preferred conditions the reaction time cannot bestated with precision but ordinarily the esterifications are completewithin 12-24 hours.

When the aromatic acid chlorides are used as reactants, generally milderreaction conditions are required. For instance, the acid chloride isordinarily added slowly to a stirred solvent solution of the alcohol ata temperature ranging from 15-50 C. After the addition is complete thereaction mixture is raised to about 60-120 C. for several hours tocomplete the reaction. The HCl byproduct can be removed by a number ofmethods including flushing the reaction mixture with an inert gas. Theuse of an inert atmosphere is not required unless an easily oxidizablesubstituent is present on the aromatic nucleus. Similarly the use ofsuperatmospheric pressure while permissible is not required.

The reaction time for esterification is shorter when the acid chloridesare used usually ranging between 2-12 hours.

When either the carboxylic acid, anhydride, ester or the acid chlorideis used as reactant, an excess of the aromatic carboxylic acid typereactant is used over that required by stoichiometry but this is not anecessity.

The isolation and purification procedures used are comparable to thatemployed in organic chemistry for isolating :and purifying esters of thealiphatic alcohols and for that reason will not be elaborated upon.Specific details appear in the embodiments and examples which follow.

In one embodiment of this invention, the neocarboranylmethyl ester ofsalicylic acid is prepared as follows:

Mix neocarboranylmethyl alcohol and salicylic acid in 300 ml. of benzenein a reaction vessel fitted with a Dean- Stark apparatus. The tworeactants are present in the ratio of 1:1.05 respectively. A catalyticquantity of ptoluenesulfonic acid is added and the reaction mixture isbrought to reflux. During 8 hours of refluxing the water is removed as awater-benzene azeotrope. The reaction mixture is cooled down, filteredand the benzene stripped oif under vacuum. The residue is treated withaqueous NaHCO to reserve unreacted salicylic acid and the ester productis recrystallized from heptane, three times to give a colorless product,whose ultraviolet and infrared spectra and elemental analysis confirmsto be the expected product.

In another embodiment, add 0.55 mole of phthalyl chloride in 50 ml. ofxylene to a stirred solution of 0.25 mole of neocarboranylbutyl alcohol(l-hydroxybutylneocarborane) in 150 ml. of xylene. After the addition iscomplete, raise the temperature to 80 C. for 4 hours. At the end of thistime flush with nitrogen and cool to room temperature and strip off thexylene under vacuum. Neutralize with an aqueous solution of 5% NaHCO andfilter to recover the desired di(-neocarboranylbutyl) ester of phthalicacid.

Another embodiment is demonstrated by the following preparation of theneocarboranyhnethyl ester of p-chlorobenzoic acid.

Slowly add a solution of 0.15 mole of p-chlorobenzoyl chloride in 100ml. of benzene to a stirred solution of 0.1 mole ofhydroxymethylneocarborane. After the addition is complete, raise thetemperature to 75-80 C. and heat for 3 hours. Flush, cool and strip offsolvent as above.

Yet another embodiment is demonstrated by the preparation of theneocarboranylethyl ester of m-ethyl benzoic acid.

To prepare this ester, add a solution of 0.25 mole of m-ethyl benzoylchloride in 100 m1. of toluene to a solution of 0.20 mole ofl-hydroxyethyl)neocarborane in 100 ml. benzene. After the addition ofacid chloride is complete, raise the temperature to 80 C. and continueheating for 6 hours. Isolate and purify the ester as above to prepare ananalytically pure sample.

Still a further embodiment is the preparation of neocarboranylmethyldi-ester of salicylic acid.

To prepare this ester, slowly add a solution of 0.25 mole ofo-hydroxybenzoyl chloride in 100 ml. of benzene to 100 ml. solution ofbenzene containing 0.10 mole of bis-(hydroxymethyl) neocarborane. Heatto 80 C. for 5 hours after the addition is complete and isolate andpurify the ester as described previously.

4 di-ester of ortho n-butyl benzoic acid is prepared as follows:

Add 0.25 mole of o butyl benzoyl chloride in 100 ml. of benzene to astirred solution of 100 ml. of benzene containing 0.10 mole ofbis-(hydroxyethyl) neocarborane. After the addition is complete, heat toC. for 6' hours. Then flush with nitrogen to remove HCl and strip undervacuum to remove benzene. Neutralize with 5% aqueous sodium bicarbonatesolution and filter to get the crude ester product. The pure ester canbe obtained by recrystallization from cyclohexane.

In comparable embodiments the following alkylcarborane esters of"benzoic and substituted benzoic acids are prepared.

To prepare carboranylmethyl salicylate (carboranylmethyl ester ofsalicylic acid), combine l-hydroxymethylcarborane (0.11 mole) andsalicylic acid (0.1 mole) and 300 ml. of benzene in the presence ofp-toluenesulfonic acid in a reaction vessel fitted with a Dean-Starkapparatus. Reflux for 6 hours and remove the water formed through thewater-benzene azeotrope. At the end of this time filter and strip olfthe benzene under vacuum. The residue is treated with aqueous sodiumbicarbonate to remove untreated salicylic acid. Recrystallize the solidester from heptane three times to give colorless, needlelike crystalsmelting 112.5-1 14 C.

Analysis.Calcd. fOI' C1OH18B1003: C, H, B, 36.72. Found: C, 40.89; H,6.54; B, 36.51.

The UV spectrum (cyclohexane) reveals two maxims:

4.48X103. 1.0 10 311.5 243.0 To prepare carboranylmethyl benzoate (thecarboranylmethyl ester of benzoic acid) mix l-carboranylmethyl alcohol(8.8 g., 0.05 mole); benzoic acid (6.1 g., 0.05 mole), p-toluenesulfonicacid 2 g., and 5 ml. of concentrated sulfuric acid in 100 ml. of benzeneand reflux for three hours, removing water formed as a water-benzeneazeotrope using the Dean-Stark trap. Cool the reaction mixture andneutralize with 10% NaHCO solution. Separate the organic layer and stripoif the solvent removed under vacuum. Recrystallize the solid residueseveral times from n-hexane to give colorless crystallinecarboranylmethyl benzoate product, M.P. -96 C.

Analysis.--Calcd. for 0 11 13 0 C, 43.42; H, 6.51; B, 38.32. Found: C,43.41; H, 6.74; B, 38.13.

The UV spectrum (cyclohexaue) reveals three maxims:

8.6X103. 9x10 1.o5 10 To prepare carboranylrnethyl[(ortho-methoxy)benzoate], heat 175 ml. of toluene containingcarboranylmethyl alcohol (8.7 g., 0.05 mole) to 65 C. under nitrogenatmosphere. To this hot solution add 9.5 g. (0.055 mole) ofortho-methoxybenzoyl chloride dropwise over a period of 15 minutes. Heatthe mixture to 75 C. for 3 hours. Flush the reaction mixture withnitrogen to remove the residual hydrogen chloride gas. Cool the reactionmixture to room temperature and remove the toluene under vacuum.Neutralize the residue with 5% sodium bicarbonate solution and filter toget the crude carboranylmethyl- (o-methoxy)benzoate, M.P. 83-85 C.Recrystallize the crude product three times from cyclohexane to givecolorless fine needles of product M.P. 86-87 C.

Analysis.-Calcd. for C H B O C, 42.7; H, 6.49; B, 35.0. Found: C, 41.67;H, 6.34; B, 34.62.

The UV spectrum (cyclohexane) reveals two maxims:

To prepare carboranylmethyl [(para-methoxy)benzoate] add 9.4 g. (0.055mole) of para-methoxybenzoyl chloride dropwise to 8.7 g. (0.05 mole) ofcarboranylmethyl alcohol in ml. toluene under nitrogen. Heat the mixturefor two hours at 100 C. and work-up the product as in the previousembodiments. A crude prod- In still a further embodiment, theneocarboranylethyl 75 uct is obtained, M.P. 98l02 C. Uponrecrystallization twice from cyclohexane a colorless fine needle-likeproduct is obtained, M.P. 102104 C.

Analysis.-Calcd. fOI' C11H2OB1OO3: C, H, 6.49- Found: C, 42.26; H, 6.59.

The UV spectrum (cyclohexane) reveals one maxim:

To obtain 1,2-bis [(o-hydroxy)benzoyloxymethyl] carborane reflux amixture of bis(hydroxymethyl)carborane (10 g., 0.05 mole), salicylicacid (15.2 g., 0.11 mole), 3 g. para-toluenesulfonic acid and 1.3 ml. ofconcentrated sulfuric acid in 150 m1. of dry benzene. After 2.0 hoursrefluxing, collect the water produced as the benzene azeo trope. Coolthe reaction mixture and strip off the solvent under vacuum. Neutralizethe residue with 3% sodium bicarbonate solution and filter to yield thecrude 1,2-bis [(o-hydroxy) benzoyloxymethyl] carborane, M.P. 166- 168 C.When recrystallized from cyclohexane a needlelike material, M.P. 175-l76C. was obtained.

Analysis.--Calcd. for C H B O C, 47.9; H, 5.45; B, 24.4. Found: c,48.01; H, 5.74; B. 24.72.

The UV spectrum (cyclohexane) reveals two maxims:

To prepare 1,2 bis[(o-rnethoxy)benzoyloxymethyl] carborane, heat 10 g.(0.05 mole) quantity of bis(hydroxymethyl)carborane in 150 m1. of drytoluene to 65 C. under a nitrogen atmosphere. Add ortho-methoxybenzoylchloride (18.7 g., 0.11 mole) dropwise over a period of 15 minutes. Heatthe mixture to '80 C. for a three hour period until the evolution ofhydrogen chloride subsides. Cool the reaction mixture to roomtemperature with continuous nitrogen sweep to remove all hydrogenchloride. Remove the solvent under vacuum, dry, and recrystallize twicefrom cyclohexane to give a colorless needle-like solid product M.P. ll02C.

Analysis.-Calcd. for C H B' O C, 51.0; H, 5.97. Found: C, 51.3; H, 6.51.

The UV spectrum (cyclohexane) reveals two maxims:

To prepare 1,2-bis[(p methoxy)benzoyloxymethyl] carborane, heat amixture of bis(hydroxymethyl)carborane g., 0.05 mole) andpara-methoxybenzoyl chloride (18.7 g., 0.11 mole) in 150 ml. of drytoluene at 75 C. for a three hour period until the HCl is evolved.Work-up the crude product, 1,2-bis[(p-methoxy)benzoyloxymethyl]carbonane, M.P. 100-102 C. and recrystallize the compound twice fromcyclohexane to yield a colorless solid. M.P. 103-l04 C.

Analysis.-Calcd. for C H B O C, 51.0; H, 5.97; B, 22.91. Found: C,50.68; H, 6.17; B, 22.67.

The UV spectrum (cyclohexane reveals one maxim:

Another representative ester which can be prepared is carboranylmethylo-toluate. This compound was prepared by refluxing a reaction mixture of0.2 mole of o-toluyl chloride, 0.2 mole of hydroxymethylcarborane and130 ml. of toluene for 6 hours. After recrystallization from heptane apure ester product was obtained whose structure was proved by elementalanalysis.

Yet another ester which can be prepared is the carboranylmethylcinnamate. This compound was prepared by refluxing a reaction mixture ofcinnamoyl chloride (0.2 mole), hydroxymethylcarborane (0.2 mole) andxylene (150 ml.) for 5 hours. After recrystallization from hexene acrystalline product was obtained whose structure was proved by elementalanalysis.

To prepare the tri-(carboranylmethyl) ester of trimesic acid(1,3,5-benzenetricarboxylic acid) heat (0.16 mole) quantity ofbis(hydroxymethyl) carborane in 150 ml. of dry toluene to 65 C. under anitrogen atmosphere. Add trimesic acid (0.05 mole) dropwise over aperiod of minutes. Heat the mixture to 80 C. for a three hour period toremove water as an azeotrope. Cool the reaction mixture to roomtemperature with continuous nitrogen sweep to remove all hydrogenchloride. Remove the solvent under vacuum, dry, and recrystallize twicefrom cyclohexane to give the purified-triester product. Elementalanalysis was used to establish the purity of the product.

To prepare the dicarboranylmethyl ester of terephthalic acid, heat amixture of bis(hydroxymethyl)carborane (0.11 mole) and terephthalylchloride (0.05 mole) in 150 ml. of dry toluene at 75 C. for a three hourperiod until the HCl is evolved. Work-up the crude diester product andrecrystallize the compound twice from cyclohexane to yield a solid whichwas shown to be the desired product by analysis.

To prepare the diester from bis-(Z-hydroxymethyl-lcarboranylmethyl)ether of benzoic acid, heat 0.2 mole of the above ether with 0.4 mole ofbenzoyl chloride in 15 0 ml. of dry toluene at C. for 4 hours untilevolution of HCl was substantially complete. Work-up andrecrystallization yielded a solid ester product which was confirmed byelemental analysis.

This invention is advantageous in both its composition and processaspects.

For example, in its composition aspect this invention offers a series ofnovel compounds useful as organic intermediates, polymer intermediatesand as additives for stabilizing materials toward ultraviolet attack.

In its process aspects, this invention ofiers several advantagesincluding good yields, flexible reaction conditions, a wide choice ofreactants and availability of these reactants. For instance, thearomatic carboxylic acid type reactants such as the preferred aromaticmonoand dibasic acids, and acid chlorides are known compounds in someinstances available in commercial quantities. The carbonane reactantssuch as the mono-hydroxyalkylcarboranes and thebis(hydroxyalkyl)carboranes can be pre pared by a number of methods.

For example, the 1,2-bis(hydroxylkyl)carborane reactants of thisinvention may be prepared by the interaction of the diacetate ester ofthe appropriate acetylenic diol and 6,9-bis(acetonitrile) decaborane toyield the 1,2- bis(acetoxyalkyl) carborane. This intermediate is thenhydrolysed is either aqueous acid or base to yield the 1,2-bis(hydroxyalkyl) carborane. For example, the lowest member of theseries, l2-bis(hydroxymethyl) carborane, is prepared by reacting1,4-diacetoXy-2-butyne with 6,9- bis(acetonitrile) decaborane until the1,2-bis(acetoxymethyl) carborane is prepared in substantial amount andthen hydrolysis with aqueous hydrogen chloride to 1,2- bis(hydroxymethyl) carborane. This diol can also be prepared by reducing1,2-bis(acetoxymethyl) carborane with lithium aluminum hydride.

The l-hydroxyalkylcarborane or mono-hyldroxyalkylcarborane reactants areprepared similarly by contacting the monoacetate esters of theappropriate acetylenic monohydric alcohol with 6,9-bis(acetonitrile)decaborane to yield the l-(acetoxyalkyl) carborane and hydrolyzing inaqueous acid or base to form the l-hydroxyalkylcarborane. For example,the lowest member of the series, l-hydroxymethyl carborane, can beprepared by reacting propargyl acetate with bis(acetonitrile) decaboraneand hydrolyzing the intermediate to the l-hydroxymethylcarborane. Adescription of the preparation of those compounds in which one or morealkyl, aryl or halogens are substituted for one or more of the boronichydrogens appears in Inorg. Chem., vol. 2, No. 6 published in December1963.

The bis(hydroxyalkyl) neocarborane reactants may be prepared among othermethods through the dilithium derivatives of neocarborane i.e.neo-Li-C-B H -C-Li. For example, bis(hydroxyethy1) neocarborane may beprepared by reacting neo-Li-C-B H -C-Li with 2 moles of ethylene oxide.The higher and lower homologues can be prepared by using the appropriateGrignard reactant of neocarborane molecule and ethylene oxide.

Similarly the mono-hydroxylneocarborane can be prepared by reacting themonolithium neocarborane (ne0 Li-C-B H -CH) or appropriate Grignardreagent with the same class of reactants, i.e. ethylene oxide.

As the numerous embodiments indicate modifications of reactionconditions, reactants and the like can be made without departing fromthe inventive concept.

While all of the ester compositions of this invention are of interest asintermediates, the preferred esters are the benzoic and salicylic estersof the hydroxyalkylcarboranes in which the alkyl group has from 1-8carbon atoms and where the aromatic nucleus can contain one or moreadditional inert substituents such as lower alkyl, lower alkoxy, halogenand hydroxy. These esters are readily prepared from commerciallyavailable aromatic acid or the acid chlorides and are good ultravioletabsorbers. These salicylic and benzoic esters are advantageous comparedto the aliphatic esters of the carborane alcohols and diole in that thearomatic esters are potent UV. absorbers and the aliphatic esters arenot. Further, the aromatic esters of this invention have much greaterthermal stability than do the corresponding aliphatic esters and forthis reason can be used as heat transfer materials where the aliphaticmaterials would be unsatisfactory.

The metes and bounds of this invention are best defined by the claimswhich follow.

We claim:

1. A benzoic acid ester of monohydroxyalkylcarboranes anddi-hydroxyalkylcarboranes, said groups having from 18 carbon atoms.

2. Carboranylmethyl benzoate.

References Cited UNITED STATES PATENTS 3,203,979 8/1965 Ager et a1.260-491 3,135,786 6/1964 Ager, Jr. et al 260-6065 3,437,688 4/1969Schwartz 260-476 CHARLES B. PARKER, Primary Examiner R. S. WEISSBERG,Assistant Examiner US. Cl. X.R.

